The present invention relates generally to a control apparatus for controlling a system of an automotive vehicle in response to sensed dynamic behavior, and more specifically, to a method and apparatus for controlling the yaw and roll motion of a vehicle.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle roll stability control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
Existing yaw stability control systems may aid in preventing a vehicle from spinning out, and hence may indirectly reduce the potential for the vehicle to have a side collision with a barrier thus reducing the likelihood of a rollover. However, due to different control objectives for yaw stability and roll stability, the standard yaw stability control system will not directly or automatically improve vehicular roll stability. Vehicle tests have shown that the standard yaw stability control system does not react properly to many on-road rollover events. One reason is that the yaw stability control system is intended to regulate both the under-steer and the over-steer of the vehicle such that during driving on abnormal road surface conditions the vehicle can still be controlled by a driver using his driving skills developed for normal road surface conditions. The roll stability control system, however, needs to make the vehicle under-steer more during the detected aggressive driving conditions that may contribute to vehicle roll instability. Intentionally making the vehicle under-steer (as required for roll stability control) and intentionally making the vehicle neutral-steer (as required for yaw stability control) are two different objectives. Notice, however, that if a near-rollover event is caused by an aggressive over-steer, the yaw stability control system might help improve roll stability due to the fact that it brings the vehicle to neutral-steer so as to reduce the amount of vehicle over-steer.
It is therefore desirable to provide an enhanced yaw stability control system such that the traditional yaw stability function is preserved and at the same time the system will directly and properly react to potential vehicular rollover events.
The present invention is particularly suitable for adding roll stability control capability to a vehicle in the standard vehicle yaw stability control system. This roll stability control function may be implemented in two ways. First, the system may be formed as a removable stand-alone function, or, second, as an integrated function with the yaw stability control strategy.
In one aspect of the invention, a control system for an automotive vehicle has a yaw rate sensor generating a yaw rate signal corresponding to a yawing angular motion of the vehicle body, a lateral acceleration sensor generating a lateral acceleration signal corresponding to a lateral acceleration of a center of gravity of the vehicle body, a steering angle sensor generating a steering angle signal corresponding to a hand-wheel angle, and four wheel speed sensors generating wheel speed signals corresponding to each rotational speed of each of the four wheels of the vehicle. A yaw stability control unit and a roll stability control unit are coupled to the yaw rate sensor, the lateral acceleration sensor, the steering wheel angle sensor, and the wheel speed sensors. The yaw stability control unit and said roll stability control unit determine a respective yaw control signal and a rollover control signal from the yaw angular rate signal, the lateral acceleration signal, the steering wheel angle signal, and the speed signal. An integration unit is coupled to the yaw stability control unit and the roll stability control unit. The integration unit determines a safety system control signal in response to the yaw control signal and the rollover control signal.
In a further aspect of the invention, a method of controlling an automotive vehicle comprises measuring a lateral acceleration of the vehicle body, measuring the yaw rate of the vehicle body, measuring a vehicle speed, which is usually a function of the wheel speed sensor signals and some calculated quantities used as standard variables in a yaw stability control system, measuring a steering wheel angle position of a vehicle hand wheel, determining a yaw control signal and a roll stability control signal as a function of the lateral acceleration, the yaw rate, steering wheel angle and the vehicle speed.
Advantageously, since the on-road roll stability function is achieved by an added control system, there is no hardware change or control structure change for the yaw stability control. The roll stability control function could also be disabled from the standard yaw stability control system through an enabling switch.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.